A SAMPLE CONTAINER

Abstract: A container is provided comprising expanded porous polytetrafluoroethylene that is used to hold a matrix with analyte that is undergoing physical, thermal, or extraction analysis. The container may be of any shape but is preferable in tubular shape having an inlet side, a sealed side, and an interior space.

Description: TITLE OF THE INVENTION A SAMPLE CONTAINER FIELD OF THE INVENTION An inert sample container is provided comprising expanded porous polytetrafluoroethylene for holding an analyte within a matrix that is to undergo analysis. The container may be employed for general chemical and clinical analyses in toxicology or general chemistry purposes; for environmental collection such as water analysis, soil analysis as well as biological analysis. BACKGROUND OF THE INVENTION The storage, transportation and actual analysis of sample analytes present significant problems requiring a great deal of time in obtaining a sample and then preparing it for the appropriate analysis. It is desirable to reduce the time and preparation necessary for such analysis including but not limited to physical, thermal and extraction analyses. In addition, some analytical techniques require samples to be held within containers during analysis which require subsequent extensive cleaning of the containers after the analysis has been completed. As an example, thermal desorption analysis requires that samples to be analyzed be placed directly into stainless steel, quartz, or glass tubes which are then placed within a chamber of the equipment. After the analysis is complete, these tubes must be thoroughly cleaned so that they may be used again. This is extremely cumbersome and ineffective as often a residue is deposited on the tube walls after the analyte has been desorbed into the vapor phase and the matrix of the analyte has been destroyed. Other tubes may have walls lined with polytetrafluoroethylene (not porous PTFE) but also require the use of additional materials such as glass wool to keep particles contained within the tubes. Such tubes cannot be sealed as purge gas must be allowed to pass through the sample. There is a need for a simple container to hold the matrix with analyte for analysis and eliminate the need for extensive cleaning of tubes. SUMMARY OF THE INVENTION An inert sample container is provided comprising expanded porous polytetrafluoroethylene for holding a matrix with analyte that is to undergo analysis wherein the container has an inlet, walls that form an interior space therein, and at least one sealed end. Preferably the expanded porous polytetrafluoroethylene has pores with an average size of between 0.1 and 20.0 μm in diameter and a porosity of between 10 and 90% and wherein the analysis may be performed at a temperature of less than 360°C. The container may have a tubular or rectangular shape. The container may be used for many different types of analysis. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of the tubular container. Figure 1a is a longitudinal cross-sectional view of the tubular container. Figure 1b is a transverse cross-sectional view of the tubular container. Figure 2 is a perspective view of a rectangular container of the present invention. Figure 2a is a longitudinal cross-sectional view of the rectangular container. Figure 2b is a transverse cross-sectional view of the rectangular container. DETAILED DESCRIPTION OF THE INVENTION A container for holding a matrix and an analyte for analysis is provided. The analyte may be in liquid, gas or solid form and the matrix holding the analyte may be soil, plastic, paper, powders, and liquid polymers. The container is preferably made entirely of expanded polytetrafluoroethylene thereby causing it to be inert so that the analyte does not become contaminated by any offgassing from the constituents of the container. Moreover because the expanded polytetrafluoroethylene is porous, volatile gasses from the analyte are able to diffuse from the container so that both the vapor portion of the analyte can be analyzed as well as any liquid portion. The matrix holding the analyte may be degraded during analysis and its residue remains within the walls of the container. The container may be constructed to be sufficiently rigid so that it is resilient and capable of holding a liquid or other amorphous shape of which matrix may assume within the container. The resiliency of the container depends on the strength and thickness of the expanded porous polytetrafluoroethylene used. The expanded porous polytetrafluoroethylene is made according to the procedures described in U.S. Patent Nos. 4,187,390 and 3,953,566. More specifically, coagulated dispersion polytetrafluoroethylene (PTFE) is lightly lubricated and extruded as a paste through an annular die extruder. In a series of heating and stretching steps, the lubricant is evaporated away and the PTFE structure is expanded such that the present void space or porosity is finally between 10 to 95% and is preferably from 70 to 85%. The material is also heated to above its crystalline melt temperature. A most preferable porosity for the material is about 70%. The selection of porosity is ultimately dependent on the properties of the materials to be analyzed so that they can be secured within the container but allow gasses to be ultimately released during analysis. The size of the individual pores can also be selected and is dependent on the properties of the matrix and analyte. Here again, the size of the pores is chosen so that vapors of the analyte may be released from the container while a liquid or solid matrix is held within the container without loss. The size of the pores may range from 0.1 to 20.0 μm. in diameter and is preferably about 3.5 μm. The size of the pores and percent porosity can be varied depending on the different conditions under which the expanded porous PTFE is made. Similarly, the wall thickness of the container may vary depending on the nature of the materials used for analysis. Generally, the wall thickness of the container is about 1mm. The container may be constructed so that it has the necessary cross- section to hold the matrix and analyte undergoing analysis. A preferable construction includes a tubular structure as shown in Figures 1, 1a and 1b wherein one end of the tube is sealed. This may be accomplished by any suitable sealing means and may include heat sealing with the use of an adhesive such as polyethylene or a melt-processible tetrafluoroethylene copolymer followed by heat and/or compression or simple fusion bonding of the walls. Ultrasonic welding may also be used. Other methods of sealing the end of the container may be accomplished by knotting or crimping. The other end of the container serves as an inlet for the materials that undergo analysis which can also be subsequently sealed or capped off with a plug of polytetrafluoroethylene or glass wool. Alternatively the inlet may be sealed shut after the matrix and analyte have been added wherein the sealing is accomplished by any of the means identified above. A third alternative is that the inlet of the container is not sealed or plugged at all but left open. Although the preferable shape of the container is tubular, there are no limitations on the shape. Thus the container may also be rectangular, square, or have some other shape as shown in Figures 2, 2a, and 2b. Any walls of the container may be sealed together by any of the means described above. In practice, several tubular containers made of expanded porous polytetrafluoroethylene were used for holding matrices consisting of contaminated soil that were to undergo thermal desorption analysis. The containers had a porosity of about 70%, pore size of about 3.5 μm. in diameter and had inner diameters of 3mm and outer diameters of 4mm. The empty containers were first preweighed and then filled with the matrix containing the analyte and reweighed. Some containers did not have the second end sealed. Other containers had both ends sealed. Each filled container was then slipped into a thermal desorption stainless steel tube and placed within the analytical chamber of the test machine (in this case - Perkin Elmer Model ATD400). The machine was then operated in accordance with standard operating procedures established by the manufacturer of the analytical equipment. The equipment ran at about 200°C with no contaminating interference from any of the tubular containers. Data of the analyte was obtained from the mass spectometer readout. After analysis was complete, the stainless steel tubes were removed from the chamber and the expanded porous PTFE tubular containers with the residual matrix of soil were easily removed from the stainless steel tubes and discarded. Although not required, the stainless steel tubes were cleaned for the next analysis. Alternatively, the containers were used to hold monomers and oligomers that were analyzed according to the procedures described above. Here the containers were particularly useful as the monomers and oligomers were extremely messy and viscous. If stainless steel tubes had been used by themselves, substantial cleaning of the stainless steel tubes after use due to the heavy residual buildup would have been required. Although the procedures described above require that the containers be used in a test environment of about 200°C, the containers are suitable for use in environments up to about 325°C for 5 minutes without any difficulty. Expanded porous PTFE containers may easily be removed from stainless steel tubes at this temperature after use. At higher temperatures (in the range from 335°C to 355 β C), the containers do not deteriorate but, forceps or other gripping means are required to remove the container from the tube. The container made solely of expanded porous polytetrafluoroethylene should not be used in temperatures above about 360°C due to thermal degradation. The containers are also believed to be particularly useful in supercritical fluid extraction wherein a matrix with analyte may be contained within the expanded porous polytetrafluoroethylene container which is then exposed to liquid carbon dioxide. The solutes may be extracted for further analysis, carbon dioxide gas may be released, and the container remains with the residual matrix. As used herein: Pore size for the material used in the container was determined by the amount of air pressure required to force liquid from the largest wetted pore of a membrane. A bubble point rating is used to determine when the largest pore yield a bubble; the larger the pore, the less pressure required to form the bubble. ASTM:F316-80 was used to determine this parameter. Porosity (% void space) was determined by density (weight per volume measurements). Wall thickness was determined by calculating the difference between the measured outer diameter of the tubular container and the measured inner diameter.

Claims: 8 PC17US94/11881 I CLAIM; 1. A container for use in holding a matrix with an analyte for analysis comprising a housing of expanded porous polytetrafluoroethylene, an inlet at one end of the housing in which the analyte is introduced into the housing, an interior space formed within the housing in which the analyte once introduced is held and at least one sealed end at the opposite end of the housing, wherein the expanded porous polytetrafluoroethylene has pores with an average size of between 0.1 and 2.0 μm in diameter and a porosity of between 10 and 95% and wherein the analysis may be performed at a temperature of no more than about 360°C. 2. A container as described in Claim 1 wherein the housing has a tubular shape. 3. A container as described in Claim 1 wherein the housing has a rectangular shape. 4. A container as described in Claim 1 for use in analysis selected from the group including physical analysis, thermal analysis and extraction. 5. A container as described in Claim 1 wherein the inlet is subsequently sealed. 6. A container as described in Claim 1 wherein the sealed end is accomplished by a sealing means selected from the group including thermal means, ultrasonic means, adhesive means, compression means, knotting and crimping. 7. A container as described in Claim 1 wherein the expanded porous polytetrafluoroethylene has pores with an average size of 3.5 μm in diameter, and a porosity of about 70%.

Inventors: NARVAEZ RICHARD, NARVAEZ, RICHARD
Applicants: GORE & ASS, W. L. GORE & ASSOCIATES, INC.
Application year: 1994
Main classification: B01L3
IPC codes: B01L3, G01N1